This invention relates generally to physiological monitors and, more particularly, to blood perfusion and pH monitors that determine the oxygenation and acidity or alkalinity in a patient's vital organs and tissues by means of induced fluorescence spectroscopy.
Early warning of the deterioration in a patient's condition largely determines the effectiveness of life sustaining critical care treatment. Tissue perfusion and oxidative metabolism may be compromised in critically ill patients in a number of pathological situations and disease states such as hemorrhage, hypoxia, septic shock, etc. This compromise often results in the redistribution of the blood flow within a patient's body which favors the brain and the heart at the expense of the skeletal muscles, kidneys and the splanchnic organs. Reduced perfusion and oxygen availability at the level of these organs may lead to ischemia which may cause tissue injury and organ failure. Also, certain conditions may lead to acidosis or alkalosis. The pH of body fluids must be maintained very near 7.4 (close to neutrality) for the body's metabolic reactions to proceed properly. Acidosis occurs if the pH falls below 7.3.
Currently, clinical techniques to monitor oxygen delivery and pH in the body rely on global metabolic measurements. Such global measurement techniques are generally unsuited for early detection and continuous monitoring of local deficiencies such as the lack of oxygen delivered to an organ.
Fluorescence spectroscopy techniques have been developed for measuring the heterogeneity of oxygen delivery to organs. Such techniques typical involve the measurement of a chemical, such as NADH, that is associated with the metabolic state of the organ. Such techniques are not widely used clinically. One reason for such limited use is the desirability of calibrating or compensating for measurement variations caused by equipment variations or the like. Such compensation typically requires careful optical splitting of the fluorescence excitation light to provide a reference light signal of known relative intensity with respect to the excitation light.
From the discussion above, it should be apparent that there is a need for a physiological medical monitor that is relatively immune to equipment variations or the like, that is simple and rapid to use, and that provides immediate results regarding a patients metabolic state. The present invention addresses these needs.